1. The Field of the Invention
The present invention relates to a method and apparatus for detecting faults in transparent material. The purpose of the invention is to determine the optical quality and detect faults in the transparent material. The transparent material indeed is a solid material, especially glass or plastic. The plastic materials include, for example, polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE) or other transparent duroplastic or thermosetting plastic, elastomeric or thermoplastic materials. The use of the invention for determination of the quality of flat glass and float glass is especially preferred.
2. Description of the Related Art
WO 99/49303 describes a method and apparatus for detection of faults in flat glass. In this method a camera observes a spot on the boundary of a two-part lighting apparatus. The lighting apparatus is embodied in two parts with red LEDs in one half and with green LEDs in the other half. Relative motion between the camera and the lighting apparatus is detected. If a beam-deflecting fault is present in the flat glass, like, e.g., a sufficiently large bubble, this fault bends the beam guided to the camera from the lighting apparatus. Because of that different amounts of the red and green light reach the wavelength-sensitive camera so that a deflection signal is produced. In this way the apparatus can detect beam-deflecting faults. Furthermore the brightness field signal is used in order to measure the size of the corresponding beam-bending or beam-deflecting fault.
The Japanese Patent Publication H 10-339795 discloses detection of faults in flat glass by introducing parallel light beams inclined to side edges of the flat glass. Because of the way in which the light beams are introduced into the interior of the strip-shaped glass material total reflection occurs, so that the light travels from one side of the flat glass to the other. If a glass fault, for example an inclusion, a knot or a bubble, is present in the interior of the flat glass, the light introduced into the volume is scattered. The scattered light is detected in this method.
DE 102 21 945.1 of May 15, 2002 discloses a similar method, in which a laser light is introduced into a flat glass piece from the side or laterally. The laser light travels from one side of the flat glass to the other because of total reflection. In this method the laser beam is introduced at the side edge of the flat glass through water into the glass. Because of the manner in which the laser beam is introduced in this method the disadvantage that there is no definite edge geometry present in float glass is overcome. In this way this latter method differs from that disclosed in the aforementioned Japanese Patent Publication in which radiation is introduced laterally into the side edge only with difficulty in a definite manner and way.